A Co(III) Complex in a Mixed Sulfur/Nitrogen Ligand Environment: Modeling the Substrate- and Product-Bound Forms of the Metalloenzyme Thiocyanate Hydrolase

Abstract

A thiolate-ligated synthetic model compound is described, which contains Co(III) in an environment resembling that of thiocyanate hydrolase (TCH). TCH catalyzes the conversion of SCN- to SCO and NH3. The five-coordinate model below reversibly binds SCN- and NH3, the substrate and product of TCH. Ligand binding induces a spin-state change from S = 1 to S = 0. Thus we show that although low-spin d6 Co(III) is usually considered to be a poor choice as catalyst, it is not so inert as to preclude ligand displacement when substrates bind trans to a thiolate.